The genus Sibinia Germar, 1817 (Coleoptera: Curculionidae: Curculioninae) includes three subgenera: Dichotychius Bedel, 1885, Microtychius Casey, 1910 and Sibinia s. str. (Skuhrovec et al., 2015). The Palaearctic S. (Sibinia) species develop in plant representatives of different genera belonging to family Caryophyllaceae [Arenaria L., Cerastium L., Dianthus L., Eremogone Fenzl, Gypsophila L., Lychnis L., Melandrium Röhl., Minuartia L., Petrorhagia (Ser.) Link, Psammophiliella Ikonn., Saponaria L., Silene L., Spergula L., Spergularia (Pers.) J. Presl & C. Presl] (Szénási, 2013; Yunakov et al., 2018). Species in subgenus Dichotychius live on Plumbaginaceae (Skuhrovec et al., 2015) and those in Microtychius have hosts belonging to different genera of family Fabaceae (Clark, 1978). Species of Sibinia are trophically associated with narrow host ranges. Some of them are monophagous whereas other are restricted to two or more plant species of a single genus. The larvae of most species feed mainly on the seeds of their hosts (Clark, 1978). Sibinia species are found in different types of habitats: salty lands, sands, xerothermic grasslands and meadows, steppes, dry and stony slopes, forest edges, agricultural habitats and salt marshes (Yunakov et al., 2018). Some species of the genus are considered as bioindicators of natural sandy habitats (Košťálová & Szénási, 2015).

Sibinia subelliptica (Desbrochers, 1873) is a Palaearctic curculionid species known from Europe, Anatolia, Siberia, East Asia (Russian Far East, N Korea, Japan, NE China) and N Africa (Algeria) (Balalaikins, 2013). It is a thermophilous oligophagous beetle that develops on plant species from the genus Dianthus, mostly in xerothermic habitats (Angelov, 1980). Its known hosts are: D. acicularis Fischer ex Ledebour (Dedyukhin & Martynenko, 2020), D. andrzejowskianus Kulcz. (Yunakov et al., 2018), D. armeria L. (Tempère & Péricart, 1989), D. balbisii Ser. (Clark, 1978), D. borbasii Vandas (Yunakov et al., 2018), D. carthusianorum L. (Cmoluch et al., 1975; Clark, 1978), D. ferrugineus Miller (Teodor, 2011), D. pratensis Bieb. (Dedyukhin, 2014), D. sylvestris Wulfen (Teodor, 2011), D. ?versicolor Fisch. ex Link (Dedyukhin, 2012). The females lay their eggs at the base of the flowers (Angelov, 1980). The complete development of the species from egg to imago takes place in the flowers of the host plant without the larva to enter the soil to pupate (Alziar, 1976), although pupation in the soil has been reported in the literature (Angelov, 1980; Tempère & Péricart, 1989). The species is common in Bulgaria from May to July from 200 to 1000 m a. s. l. (Angelov, 1980).

The genus Dianthus L. (Caryophyllaceae) is represented by annual, biennial and perennial herbaceous plants (Kirillov et al., 2016). It is widespread mainly in Europe, the Mediterranean region and in Asia, and a few species are known from Africa and America (Chandra et al., 2016). Dianthus giganteus d’Urv. is a perennial plant that grows on stony and grassy places in the lowlands and mountains. It occurs throughout Bulgaria up to 2100 m a. s. l. It is also distributed in Albania, former Yugoslavia, Greece, Italy, Romania, Turkey and SW Asia (Stojanov, 1966).

There is no information in the literature about parasitoids of the curculionid beetle S. subelliptica. The aim of this study is to provide the first data on a parasitoid complex probably associated with this weevil.

Over 2100 dry inflorescences of D. giganteus were collected on 1.VIII.2015 and on 15.VII. 2016 in Arbanasi Village near Veliko Tarnovo (43°05’50.1” N 25°40’38.3” E, 417 m). The collected material was stored in laboratory conditions in plastic bottles darkened with an aluminium foil and with an additional transparent tube at temperature 23-26° C. The tops of the bottles were cut out and covered with white cheesecloth. The material was stored for at least one year until all emergences had ceased. Emerged parasitoids were aspirated with a pooter, fixed in ethanol and later examined under a stereo microscope. During the dissection of at least 300 inflorescences, we found 500 imagos of S. subelliptica at the base of the flowers (Fig. 1). Only 12 specimens were observed outside the inflorescences.

The weevil and its parasitoids were identified following Graham (1969, 1987, 1991), Angelov (1980), Grissell (1995), Zerova & Seryogina (1999), Zerova (2010), Gibson & Fusu (2016), Fusu (2017) and Fursov et al. (2019).

The specimens are preserved in the authors’ collection (University of Plovdiv and Institute of Biodiversity and Ecosystems Research, Bulgarian Academy of Sciences).

Colour photographs were taken with a Canon 5D Mark III digital camera.

During the study we reared 512 specimens of S. subelliptica, along with 905 specimens of hymenopteran parasitoids belonging to 11 species (Table 1) of five families of Chalcidoidea (Eulophidae, Eupelmidae, Eurytomidae, Pteromalidae and Torymidae), from inflorescences of D. giganteus (Fig. 2).

Since only 1/7 of the inflorescences were dissected, the number of beetles in them can be expected to exceed 3500 individuals. In addition to these, we obtained hundreds of thrips (Thysanoptera) and four specimens of unidentified species of Chrysopidae (Neuroptera). Whilst S. subelliptica was not proven to be the host species of all these parasitoids, we believe that it was very probably the host (primary or secondary) of at least the most frequently reared Hymenoptera. Two of the parasitoid species, Eurytoma coleophorae and E. coleopterae, are recorded for the first time from Bulgaria. All parasitoids are suggested to be associated with S. subelliptica for the first time and, with the exception of E. barai and E. microzonus, all parasitoid species are newly associated with D. giganteus. Also, D. giganteus is recorded here as a new host plant of S. subelliptica.

Although we cannot conclusively confirm that all reared parasitoids are primary parasitoids of S. subelliptica, their large number (with the exception of C. crassiceps and E. coleophorae) suggests a more common than accidental association with this host.

The review of the literature shows that there are no data about parasitoids of S. subelliptica. However, parasitoids belonging to four families of Chalcidoidea (Eulophidae, Eupelmidae, Eurytomidae and Pteromalidae) and one family of Ichneumonoidea (Braconidae) have been recorded on eight other Sibinia spp. (Table 2).

Aprostocetus venustus is a parasitoid of species of Bruchophagus Ashmead (Hymenoptera: Eurytomidae) in seeds of Fabaceae (Graham, 1987; Boyadzhiev, 2006; Ribes Escolà & Askew, 2009) as well as of species of Contarinia Rondani (Diptera: Cecidomyiidae) in Sorghum (Poaceae) [as Tetrastichus venustus Gahan] (Wiseman et al., 1978) and Mango (Anacardiaceae) (Yefremova et al., 2007). It has been also reared from Dasineura oleae (Angelini) (Diptera: Cecidomyiidae) on Olea europaea L. (Oleaceae) (Doganlar, 1992). Recently, A. venustus was reared from flower heads of Xeranthemum annuum L. (Asteraceae) along with Larinus sibiricus Gyllenhal (Coleoptera: Curculionidae) and a rich complex of hymenopteran parasitoids associated with this beetle (Antov et al., 2020). We found no information in the literature for previous rearings of this eulophid species from D. giganteus.

Baryscapus Förster, 1856 is a large and biologically diverse genus in the subfamily Tetrastichinae (Eulophidae) (Graham, 1991) comprising 128 species with a cosmopolitan distribution (Noyes, 2019). Species of the genus develop mostly as gregarious or more rarely as solitary endoparasitoids of larvae or pupae of a wide variety of insect hosts belonging to Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera and Neuroptera. Some species of Baryscapus are secondary parasitoids of species of the families Braconidae and Ichneumonidae and of the superfamilies Chalcidoidea and Cynipoidea (Graham, 1991). We assume that Baryscapus sp. near garganus is an undescribed species and differs from females of B. garganus mainly in structure of antennae and thorax as well as the longer abdomen. Its taxonomic characterization will be a subject of further studies.

Eupelmus barai is a polyphagous parasitoid whose host range include various insects belonging to Coleoptera (Curculionidae), Diptera (Cecidomyiidae and Tephritidae), Hymenoptera (Cynipidae, Diprionidae and Eurytomidae) and Lepidoptera (Coleophoridae, Millieridae, Tortricidae and Yponomeutidae). In the family Curculionidae, only Scolytus rugulosus (Müller) has been recorded as its host from Moldova (Fusu, 2017).

Eupelmus microzonus is a polyphagous parasitoid attacking the larvae and pupae of a wide range of insect hosts that are usually concealed in galls, flower heads, seeds, grass stems or cocoons and belong to Coleoptera, Diptera, Hymenoptera and Lepidoptera (Bouček, 1977; Antov & Stojanova, 2020). The following curculionid beetles are known as its hosts: Anthonomus pomorum (Linnaeus) (Gibson & Fusu, 2016), Ceutorhynchus obstrictus (Marsham) (Haye et al., 2018), Curculio glandium Marsham (Kostjukov et al., 2018), Microlarinus lareynii (Jacquelin du Val) (Soydanbay-Tunçyürek, 1976), Pachytychius hordei (Brullé) (Gözüaçık & Şimşek, 2015), Tychius aureolus Kiesenwetter [= T. femoralis Brisout] and T. flavus Becker (Nikolskaya, 1952). Recently, the species was also associated with L. sibiricus (Antov et al., 2020). It has been recorded as a parasitoid of three weevil species of the family Brentidae: Catapion seniculus (Kirby) [= Apion seniculus Kirby] (Mambetova, 1975, as cited by Noyes, 2019), Hemitrichapion reflexum (Gyllenhal) (Muhtarova et al., 2009) and Oxystoma ochropus (Germar) (Lotfalizadeh & Hashemi, 2015).

Aximopsis augasmae has been recorded as a parasitoid of the larvae of Augasma atraphaxidellum Kuznetzov (Lepidoptera: Coleophoridae) on Atraphaxis spinosa L. (Polygonaceae) and some other moth species on Zygophyllum L. (Zygophyllaceae) (Zerova & Seryogina, 2006). It was also reported as a parasitoid of Etiella zinckenella (Treitschke) (Lepidoptera: Pyralidae) in pods of Sophora alopecuroides L. (Fabaceae) (Lotfalizadeh & Hosseini, 2014). There is no data for its rearing from D. giganteus.

Aximopsis collina has been recorded as a parasitoid in Diplolepis galls on Rosa spp. (Lotfalizadeh et al., 2006; Zerova, 2010; Mete & Mergen, 2017). Recently, it was associated with seeds of three Asphodelus spp. (Delvare et al., 2019). There is no data for its rearing from D. giganteus.

Eurytoma coleophorae has been reared from galls of Coleophora serinipennella Christoph (Lepidoptera: Coleophoridae) on Atriplex sp. (Amaranthaceae) and Ascalenia kabulella Kasy (Lepidoptera: Cosmopterigidae) on Myricaria alopecuroides Schrenk (Tamaricaceae) (Zerova, 2010). There is no data for its rearing from D. giganteus. The species is distributed in SE Europe and Kyrgyzstan (Zerova, 2010). This is the first record from Bulgaria.

Eurytoma coleopterae is a parasitoid attacking the larvae of small beetles whose development takes place in stems, galls and seeds of herbaceous plants (Fursov et al., 2019). The species has been reared from larvae of Lixus salsolae Faust. and Sibinia femoralis Germar (Coleoptera: Curculionidae) in galls on Silene wolgensis (Hornem.) Otth [= Otites wolgensis (Hornem.) Grossh.] (Caryophyllaceae) (Zerova, 1978). Recently, it was obtained from larvae of Metapion sp. (Coleoptera: Curculionidae) developing in seeds of Ruta sp. (Rutaceae) (Fursov et al., 2019). In the family Caryophyllaceae, this species is associated with S. wolgensis, but not with D. giganteus. It is known from Turkey, Turkmenistan and Ukraine (Fursov et al., 2019), but it has not been recorded from Bulgaria so far.

Catolaccus crassiceps is a polyphagous species that develops as a primary or secondary parasitoid on a wide variety of insect hosts belonging to Coleoptera (Curculionidae), Hymenoptera (Braconidae and Cynipidae), Lepidoptera (Coleophoridae, Crambidae, Gelechiidae, Noctuidae, Nolidae and Pieridae) and Neuroptera (Chrysopidae) (Dzhanokmen, 2017). It has been reared from cocoons of Coniatus indicus Marshall (Coleoptera: Curculionidae) on Tamarix dioica Roxb. ex Roth (Tamaricaceae) (Boućek et al., 1978). In the family Caryophyllaceae, this species is associated with Gypsophila struthium Loefl. (Askew et al., 2001), but not with D. giganteus.

Pteromalus ochrocerus is known as a parasitoid on species of Curculionidae (Coleoptera), Cynipidae (Hymenoptera) and Tephritidae (Diptera) (Cobo et al., 2016). Its host among the curculionid beetles is A. pomorum (Thompson, 1958). Plant associations include Asteraceae and Lamiaceae (Askew et al., 2006; Cobo et al., 2016), but not Caryophyllaceae.

Exopristus trigonomerus is a parasitoid of species of Coleoptera and probably Diptera concealed in galls and stems of herbaceous plants. Its known hosts among the curculionid beetles are: Rhinusa bipustulata (Rossi) [= Gymnetron bipustulatum (Rossi)] (Zerova & Seryogina, 1999), Larinus canescens Gyllenhal (Cobo et al., 2014), L. sibiricus (Antov et al., 2020) and P. hordei (Altınayar, 1981). It has been also obtained from larvae of the apple fruit weevil Tatianaerhynchites aequatus (L.) (Coleoptera: Rhynchitidae) in Turkey (Bolu, 2006). Plant associations include Asteraceae, Cistaceae, Fabaceae, Gnetaceae, Papaveraceae, Scrophulariaceae (Noyes, 2019) and Plantaginaceae (Bouček, 1977), but not Caryophyllaceae. In our study, E. trigonomerus is the most numerous parasitoid with 189 specimens reared in 2015 and 156 specimens in 2016.